A hand-held device that can evaluate the ripeness of different varieties of apples is presented in Scientific Reports this week. The spectrometer, which weighs 48g, works with an application on a smartphone via a wireless connection, to collect, store and analyse data from the device.

Optical spectroscopy - a technique in which the properties of objects can be studied based on their interactions with light - has a number of applications including assessing food quality, environmental sensing and pharmaceutical testing. However, most spectrometers used in industrial- or laboratory-based applications are expensive, bulky and require an accompanying computing device to capture data. Previous research has produced portable smartphone spectrometers; however, the data they provide has been inconsistent.

Anshuman Das and colleagues created a prototype spectrometer 88mm x 37mm x 22mm in size, with a dedicated application interface on a smartphone. The authors then used the spectrometer to evaluate the ripeness of three different varieties of apples - Golden Delicious, Empire and McIntosh. This was done by measuring the UV fluorescence from chlorophyll present in the skin of the apples during the ripening process over a period of 11 days, and their results correlated with destructive firmness tests on the fruit.

The authors argue that optical tests that are non-destructive, such as the one their device performs, could assist farmers in determining optimum harvest times. They also suggest the device could be adapted for consumer applications for testing fruit ripeness.